QA and fixes

• Update Slovak translation thanks to @dodog
• Update Portuguese translation thanks to @marcelocripe
• Add CI for the macOS and MSYS2 targets
• Avoid panic on broken output pipe (#209, PR #353)
• Don't have the app window briefly show when starting in background mode (#363)
• Fix migration from old SongRec versions on Windows (#355, PR #356)
• Add GUI option to retain window size across restarts (#160, PR #357)
• Fix sanitizing history and preferences files on disk operations (PR #366, #362, #371)
• Support for systems with non UTF-8 paths thanks to @HarpeLm
• QA, unit tests, safety checks, thanks to @HarpeLm